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If I turn on the hot water in my shower with limited flow (not a trickle, but not a gush), within a minute the flow slows to a trickle and it starts making a rapidly-repeating banging noise that doesn't stop until it's turned off or the flow is increased. Cavitation, water hammer, or something else? arimareiji ( talk) 00:13, 25 February 2009 (UTC)
why is AgNO3 kept in coloured bottles??? —Preceding unsigned comment added by 123.50.168.74 ( talk) 13:15, 25 February 2009 (UTC)
Silver nitrate used to be used for photographic work - so it is indeed sensitive to light. But the main reason it was replaced is because it's not sensitive enough for dim light or short exposures. So it's RELATIVELY insensitive (compared to other photosensitive substances) - but a dark glass jar is good enough. SteveBaker ( talk) 16:39, 25 February 2009 (UTC)
Hello I heard that when there is very high electric tension (eg 1000000 Walt), there is no longer a risk to humans. 1 Is it true? 2 What is the explanation for this phenomenon?
In the article Electric shock it is written that the danger is primarily in the tensions between 30 and 250 volt, it may be related to the subject.
Thank you very much —Preceding unsigned comment added by 82.81.19.138 ( talk) 13:26, 25 February 2009 (UTC)
I think there is a fundamental confusion here. The risk due to touching - or even getting within a few feet of a high tension power cable is most definitely very high indeed. What I think the OP is referring to is that it is (perhaps) no longer considered dangerous to live, work or generally be close to high tension power lines. There has been much controversy over this in the past where people who live or work close to these gigantic pylons have complained of a variety of long-term medical conditions that have been loosely attributed to some aspect of those power lines. There has been more talk of this in the media quite recently because the 'Obama stimulus package' includes a boatload of cash for creating a much improved electrical grid throughout the USA in order to allow far distant wind and solar power plants to distribute their power all across the country - even though they are (by necessity) situated in fairly remote an/or inhospitable places. This huge build-out of new high tension power lines will doubtless upset a great many people - and the debate as to whether they are safe or harmful over the long term has resurfaced. However, there is absolutely no doubt that if you get within some short distance of the cable itself, you could come to a great deal of harm! SteveBaker ( talk) 16:36, 25 February 2009 (UTC)
The prime element in the lethality of electricity is the internal resistance of the voltage source. If internal resistance is high, only a small amount of current can flow in an external circuit. It is current that harms a person. A high voltage can impose a shock, but will not cause harm if the internal resistance of the voltage source is high. There are other factors involved, such as the amount of sweat on the skin, place of contact, etc. But internal resistance is the prime element. The internal resistance of a voltage source is often overlooked. For instance, the Wikipedia articles "Cattle prod", "Electric shock", "Electroshock weapon", and "Taser" make no mention of it. Also, electronic discussions in general often ignore the internal resistance of a voltage source when it should be mentioned. – GlowWorm. —Preceding unsigned comment added by 98.16.66.64 ( talk) 17:25, 25 February 2009 (UTC)
(First off, why isn't there a Medical section of the RD?)
If someone with CIPA (the inability to feel pain) got stabbed in the heart, would they still live since there's no pain to kill them? -- 129.130.239.68 ( talk) 15:50, 25 February 2009 (UTC)
Well, no. You see, all of those are indirect causes of death associated with pain:
In each example you cite it's not the pain that's primarily responsible for death. It's associated, sure, but ultimately it's our response that determines the consequences. Hence my earlier assertion: no one ever dies from pain alone. Matto paedia Have a yarn 02:43, 28 February 2009 (UTC)
Over at the colors of noise article, there are several images of power spectra of the various "colors". While I am not an expert in these I do know the difference between white and pink noise. When I looked at their respective spectra images however, what was called white noise was flat on a logarithmic scale, yet that is the definition of pink noise. I am afraid that several other images may be wrong as well. Could someone with some expertise here check out those images and figure out what needs to be fixed? Thanks, Baccyak4H ( Yak!) 17:50, 25 February 2009 (UTC)
Hi. Now, I realise that there really aren't really any strict definitions for a "continent", but let's look at it from a scientific prespective. I know that areas with a single continental shelf is often defined as a continent (but Europe, Asia, and Africa are considered individual continents, and the Americas are split into North and South America), and areas with separate tectonic plates are often considered one continent (as is the case with Asia, India, and Indonesia). However, what I really mean is, do we really know if Antarctica consists of a single tectonic plate, or if there were rifts resulting from a collision of landmasses that stayed together ever since? Old rifts and plate edges could easily have degraded over geologic time, but areas like the New Madrid Fault and the Appalachian Mountains in North America still cause earthquakes today, even though they are both over 100 million years old. One of my hypotheses is that there are far more rifts, faults, and plate boundaries than we know of, even if they don't reach from the surface to the mantle. So, this would make even tectonic plates not have a strict definition. However, could some of these pseudo-boundaries be responsible for some subglacial and other Antarctic features, such as the Transantarctic mountains, Ellsworth Mountains, the mountains east (clockwise) of the Ross Ice Shelf, some Antarctic Volcanoes (I know some are probably caused by hot spots, but hot spots require a weak spot in the crust above the mantle, doesn't they? Also, no tectonic boundaries are known to extend as far south as the continent itself), the Bentley Subglacial Trench, the Gamburtsev Mountain Range? I know that ice can be partly responsible for many great features (such as the Great Lakes), but the ice should act to smooth out the contrasts in elevation, not enhance them. The Gamburtsev Mountains especially seem similar to the Alps in topography, but also potentially in how they formed. Why is this such a mystery? Wasn't that part of East Antarctica supposed to have collided with Australia around the time those mountains were formed, and if not, then could additional plate boundaries be responsible? Could the stress of ice create some new fractures, and if the ice is lifted, could others potentially form (this would imply that global warming could cause earthquakes, because if it can quickly relieve stresses in the crust, why couldn't it cause earthquakes as well)? Do we just assume Antarctica is a single plate with no rift zones or other faults simply because the entire region is covered by a single ice cap that extends to the bottom of the ocean, and because we simply don't have enough information? Thanks. ~ A H 1( T C U) 23:06, 25 February 2009 (UTC)
Science desk | ||
---|---|---|
< February 24 | << Jan | February | Mar >> | February 26 > |
Welcome to the Wikipedia Science Reference Desk Archives |
---|
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages. |
If I turn on the hot water in my shower with limited flow (not a trickle, but not a gush), within a minute the flow slows to a trickle and it starts making a rapidly-repeating banging noise that doesn't stop until it's turned off or the flow is increased. Cavitation, water hammer, or something else? arimareiji ( talk) 00:13, 25 February 2009 (UTC)
why is AgNO3 kept in coloured bottles??? —Preceding unsigned comment added by 123.50.168.74 ( talk) 13:15, 25 February 2009 (UTC)
Silver nitrate used to be used for photographic work - so it is indeed sensitive to light. But the main reason it was replaced is because it's not sensitive enough for dim light or short exposures. So it's RELATIVELY insensitive (compared to other photosensitive substances) - but a dark glass jar is good enough. SteveBaker ( talk) 16:39, 25 February 2009 (UTC)
Hello I heard that when there is very high electric tension (eg 1000000 Walt), there is no longer a risk to humans. 1 Is it true? 2 What is the explanation for this phenomenon?
In the article Electric shock it is written that the danger is primarily in the tensions between 30 and 250 volt, it may be related to the subject.
Thank you very much —Preceding unsigned comment added by 82.81.19.138 ( talk) 13:26, 25 February 2009 (UTC)
I think there is a fundamental confusion here. The risk due to touching - or even getting within a few feet of a high tension power cable is most definitely very high indeed. What I think the OP is referring to is that it is (perhaps) no longer considered dangerous to live, work or generally be close to high tension power lines. There has been much controversy over this in the past where people who live or work close to these gigantic pylons have complained of a variety of long-term medical conditions that have been loosely attributed to some aspect of those power lines. There has been more talk of this in the media quite recently because the 'Obama stimulus package' includes a boatload of cash for creating a much improved electrical grid throughout the USA in order to allow far distant wind and solar power plants to distribute their power all across the country - even though they are (by necessity) situated in fairly remote an/or inhospitable places. This huge build-out of new high tension power lines will doubtless upset a great many people - and the debate as to whether they are safe or harmful over the long term has resurfaced. However, there is absolutely no doubt that if you get within some short distance of the cable itself, you could come to a great deal of harm! SteveBaker ( talk) 16:36, 25 February 2009 (UTC)
The prime element in the lethality of electricity is the internal resistance of the voltage source. If internal resistance is high, only a small amount of current can flow in an external circuit. It is current that harms a person. A high voltage can impose a shock, but will not cause harm if the internal resistance of the voltage source is high. There are other factors involved, such as the amount of sweat on the skin, place of contact, etc. But internal resistance is the prime element. The internal resistance of a voltage source is often overlooked. For instance, the Wikipedia articles "Cattle prod", "Electric shock", "Electroshock weapon", and "Taser" make no mention of it. Also, electronic discussions in general often ignore the internal resistance of a voltage source when it should be mentioned. – GlowWorm. —Preceding unsigned comment added by 98.16.66.64 ( talk) 17:25, 25 February 2009 (UTC)
(First off, why isn't there a Medical section of the RD?)
If someone with CIPA (the inability to feel pain) got stabbed in the heart, would they still live since there's no pain to kill them? -- 129.130.239.68 ( talk) 15:50, 25 February 2009 (UTC)
Well, no. You see, all of those are indirect causes of death associated with pain:
In each example you cite it's not the pain that's primarily responsible for death. It's associated, sure, but ultimately it's our response that determines the consequences. Hence my earlier assertion: no one ever dies from pain alone. Matto paedia Have a yarn 02:43, 28 February 2009 (UTC)
Over at the colors of noise article, there are several images of power spectra of the various "colors". While I am not an expert in these I do know the difference between white and pink noise. When I looked at their respective spectra images however, what was called white noise was flat on a logarithmic scale, yet that is the definition of pink noise. I am afraid that several other images may be wrong as well. Could someone with some expertise here check out those images and figure out what needs to be fixed? Thanks, Baccyak4H ( Yak!) 17:50, 25 February 2009 (UTC)
Hi. Now, I realise that there really aren't really any strict definitions for a "continent", but let's look at it from a scientific prespective. I know that areas with a single continental shelf is often defined as a continent (but Europe, Asia, and Africa are considered individual continents, and the Americas are split into North and South America), and areas with separate tectonic plates are often considered one continent (as is the case with Asia, India, and Indonesia). However, what I really mean is, do we really know if Antarctica consists of a single tectonic plate, or if there were rifts resulting from a collision of landmasses that stayed together ever since? Old rifts and plate edges could easily have degraded over geologic time, but areas like the New Madrid Fault and the Appalachian Mountains in North America still cause earthquakes today, even though they are both over 100 million years old. One of my hypotheses is that there are far more rifts, faults, and plate boundaries than we know of, even if they don't reach from the surface to the mantle. So, this would make even tectonic plates not have a strict definition. However, could some of these pseudo-boundaries be responsible for some subglacial and other Antarctic features, such as the Transantarctic mountains, Ellsworth Mountains, the mountains east (clockwise) of the Ross Ice Shelf, some Antarctic Volcanoes (I know some are probably caused by hot spots, but hot spots require a weak spot in the crust above the mantle, doesn't they? Also, no tectonic boundaries are known to extend as far south as the continent itself), the Bentley Subglacial Trench, the Gamburtsev Mountain Range? I know that ice can be partly responsible for many great features (such as the Great Lakes), but the ice should act to smooth out the contrasts in elevation, not enhance them. The Gamburtsev Mountains especially seem similar to the Alps in topography, but also potentially in how they formed. Why is this such a mystery? Wasn't that part of East Antarctica supposed to have collided with Australia around the time those mountains were formed, and if not, then could additional plate boundaries be responsible? Could the stress of ice create some new fractures, and if the ice is lifted, could others potentially form (this would imply that global warming could cause earthquakes, because if it can quickly relieve stresses in the crust, why couldn't it cause earthquakes as well)? Do we just assume Antarctica is a single plate with no rift zones or other faults simply because the entire region is covered by a single ice cap that extends to the bottom of the ocean, and because we simply don't have enough information? Thanks. ~ A H 1( T C U) 23:06, 25 February 2009 (UTC)